at a certain point all you need is reputable sources pointing at the percentage of these too low to be true goods being fake listings before you go even if i bought 3 at least one of them will be real and it'll still be an absolute bargain.
This being due to the fact that things have a percieved price floor. While a 3090 seem impossible to be 400 and therefore people would not buy at, the two things that a seller can do is raise it to a price the market isn't paying and hold it or sell it off by a factor less that will tempt people to take the gamble.
There will be people who get things from deceased estates for example just wanting to dump everything and not deal with the hassle of finding a place for it or managing it until it eventually can be moved.
It's simply a case of percentage validity at that point.